This invention relates to monitoring of pollutants in a gas, and more particularly to a new and improved system and method for specifying the pollutants and monitoring the concentrations thereof in both the gaseous and aerosol phases.
One area of use of the present invention is monitoring sulphate aerosols in the ambient atmosphere, although the principles of the invention can be variously applied. An aerosol is an aggregate of solid or liquid matter dispersed in the air, and specific aerosols such as sulphates of a size range from about 0.1 micron to about 2.0 microns are considered to be harmful to health. In particular, such particles are not filtered out by the human body whereas larger sizes are filtered out and smaller sizes are believed not to be harmful.
Several problems are associated with methods employed for measurement of aerosol pollutants which involve first, a collection phase where the airborne particles are collected on filters and second, an analytical phase where measurements of the collected particles are made. During the first phase, interparticle reactions may occur on the filter collecting surfaces especially since the particle concentrations are enhanced considerably by collection. With sulphate aerosols, H.sub.2 SO.sub.4 and (NH.sub.4).sub.2 SO.sub.4 are believed to be the major sulfur constituents, and increasing the concentrations of the chemically reactive H.sub.2 SO.sub.4 and (NH.sub.4).sub.2 SO.sub.4 from dilute atmospheric to a concentrated surface deposit on a filter leads to chemical interactions. In addition, SO.sub.2 can be converted to HSO.sub.4.sup.- and SO.sub.4.sup.= by catalytic interaction with other particles collected on the filter. Briefly, the aerosols may interact chemically with each other, the filter media, and the ambient gases, e.g., SO.sub.2 and NH.sub.3, passing through the filter. Therefore, the data resulting from the second phase are not necessarily indicative of the original aerosol concentration. Furthermore, the second phase usually takes place in a laboratory rather than at the monitoring site so that real-time analysis of pollutant concentration is not possible.